Freshwater SawfishPristis microdon
Sawfish look a lot like sharks but they are modified rays, and their snouts (rostrum) are studded, not with teeth, but with specialized denticles, which are a type of scale. Freshwater sawfish have larger 'teeth' on their rostrum than many other sawfish, and they generally grow to be almost 20 feet long. Seasonally they live far up rivers and into freshwater lakes, and then move to estuaries, bays, and some coastal marine areas. Undisturbed, sawfish are considered harmless to humans, but conversely their population is threatened by bycatch and pollution issues.
Order - Pristiformes
Family - Pristidae
Genus - Pristis
Species - microdon
Common English names for the freshwater sawfish include: common sawfish, greattooth sawfish, largetooth sawfish, Leichthardts sawfish, and wide snouted saw fish. Other common names for the freshwater sawfish include: Araguaguá, peixe-serra, & tubarão-serra (Portuguese), barabad (Kuyunon), barasan & pakangan (Bikol), barasan & tag-an (Tagalog), buntok lagari (Kapampangan), cá dao (Vietnamese), caixaô (Sena), catanuda, dienton, pejesierra, pez peine, pez rastrillo, & seirra (Spanish), chinyabanga & kashua (Zimbabwe-local dialects), cucut gergaji, cucut pedang, panprang, parampang, pemperang, & prampran (Malay), cucut krakas, mungsing, panprang, parampang, pemperang, prampang, & prampran (Javanese), ferskvandssavrokke (Danish), galwanyi (Bunuba & Gooniyandi Aboriginals), groottand-saagvis (Afrikaans), khandere & shinshi (Marathi), kleingezahnter sägefisch & Leichthardts sägefisch (German), krarin (Sranan), kumben-sorah & makarasravu (Malayalam), kundah (Oriya), nga-man-swethi (Burmese), nokogiriei (Japanese), palangan (Pangasinan), papa upanga (Swahili), pial pial & wirridanyniny (Nyikina Aboriginal), poisson-scie grandent (French), serra (Creole dialect of Portuguese), taghan (Visayan), trey thka & trey thkaw (Khmer), valameen (Tamil), wirrdani (Walmajarri Aboriginal), and zoetwaterzaagrog (Dutch).
Importance to HumansLandings of the freshwater sawfish are usually accidental, as they are caught in various commercial and local gillnet, trawl, and hook and line fisheries targeting other species. Like all sawfishes, freshwater sawfish can be utilized as meat for human consumption, their fins sold into the Asian 'shark fin' market, their livers processed for oil, and their skins can made into leather. In addition, the eggs, liver oil, and bile of sawfishes can be used in Chinese traditional medicine. Also, like all other sawfishes, their rostra may be used in traditional medicine, as religious offerings, and sold as curios. There is little or no indication of utilization of this species as food anywhere in its range. Freshwater sawfish provide an available food source for indigenous peoples of Western Australia.
This species is occasionally sought after as a game fish using rod and reel, as seen in South Africa and in Queensland, Australia. Although large freshwater sawfish are capable of long and stubborn fights even on heavy tackle, this species lacks the aerial acrobatics and swiftness that adds to the appeal of more typical game fish. The International Game Fish Association does not have a record holder for the freshwater sawfish.
Danger to HumansThe freshwater sawfish, like all sawfishes, is harmless to humans if left undisturbed. Humans are too large to be viewed as potential prey. Care must be taken when handling or approaching a sawfish of any size, as they may defend themselves when they feel threatened, using their rostrum to strike from side-to-side with considerable force. The freshwater sawfish attains a large size and is equipped with a very wide rostrum sporting large teeth. For these reasons, extra care should be afforded when encountering this species.
The status of the freshwater sawfish populations is currently unknown, and no effective legislation exists to protect this species. However, The World Conservation Union (IUCN) Red List of Threatened Species categorizes this species as "Critically Endangered". Further, freswater sawfish are listed under Appendix II of the Convention on the International Trade of Endangered Species (CITES), permitting only the sale of live freshwater sawfish from Australia to aquaria to promote education and conservation efforts. It is thought that the species has experienced significant population declines in many portions of its range. This is due to its extreme vulnerability as bycatch in nearshore and freshwater gillnet and hook and line fisheries. In northern Australia, this species is particularly vulnerable as bycatch in fisheries targeting barramundi (Lates calcarifer) and threadfins (Polynemidae), and it is landed in Queensland fishing tournaments. It is also caught accidentally in Natal and Durban (South Africa) anti-shark nets. Other impacts likely include human-induced habitat modification and pollution of inshore coastal waters, estuaries, and river systems. Examples include the Camballin Barrage in the Fitzroy River (Western Australia) where migrating freshwater sawfish appear to be negatively impacted. In addition, this species is susceptible to entanglement in anthropogenic debris, including discarded fishing line, resulting in injury or possibly death.
Geographical DistributionIn Africa, the freshwater sawfish occurs along the eastern coastline from at least as far south as Port Alfred (south of Durban), commonly ascends the Zambezi River, is found off Madagascar, occurs at Zanzibar and probably ranges north to Somalia. The presence of the freshwater sawfish in the Red Sea and as far north as the Mediterranean Sea needs confirmation. This species is found off Pakistan and India, where it has been recorded far upriver in freshwater. In the eastern Indian Ocean, the species ranges from the East Indies and Thailand to Indonesia and Australia (from western Australia to the northern territory and Queensland). The freshwater sawfish occurs off Vietnam in the South China Sea, throughout the Philippines (where the local population appears to have greatly declined), south through Borneo and east to Papua New Guinea.
Examples of inland water bodies where it has been documented include the Zambezi River (east Africa), 40 miles (64.4 km) up the Mahanudde River (India), 38.5 miles (62.0 km) up the Menam Chao Phya River (Thailand), Mekong River below Khone Falls (Thailand and Laos), the Fly River and Lake Murray (Papua New Guinea), and the Daly, Gilbert, and Sepik rivers (northern Australia).
This species is well known to occur far up river systems, including contiguous lakes and ephemeral ponds (Australia), where it lives in freshwater conditions. Freshwater sawfish in northern Australia seem to prefer these freshwater habitats during the wet season (December-March). During the dry season (May-October), Australian freshwater sawfish seem to prefer estuaries and bays, along with coastal marine habitats. The freshwater sawfish shares similar habitat preferences with the bull shark (Carcharhinus leucas), and these two species can often be found occupying the same water bodies. Mature individuals may, at least seasonally, utilize deeper offshore marine habitats.
All sawfishes are highly modified and elongate rays having a shark-like body and a blade-like snout (termed 'rostrum') that has lateral, tooth-like denticles (termed 'rostral teeth') set into sockets. The presence of a rostrum having laterally protruding teeth separates sawfishes from all other skates and rays.
The freshwater sawfish can be distinguished from sawsharks (Pristiophorus spp.) by its lack of barbels, dorso-laterally compressed body, ventrally located gills (not laterally), large size, preference for shallow water habitats, and its similarly-sized rostral teeth.
The rostral teeth of the freshwater sawfish are particularly massive compared to those of other sawfishes, except that of the largetooth sawfish (Pristis perotteti). The rostral tooth count for freshwater sawfish varies between 14 and 23 (typically 18-20) per side. The rostral teeth may number more on one side of the rostrum than the opposing side in this species, the left side usually having the greater number. In two separate studies, researchers found a significant difference in the numbers of rostral teeth per side in males compared with that of females (termed 'sexual dimorphism'). In both studies, males appeared to have a greater average tooth count per side than did females (males average 20.9, females average 18.9), regardless of geographic area. Male freshwater sawfish may have slightly longer rostra than do females of the same total length.
The freshwater sawfish is distinguished from the knifetooth sawfish (Anoxypristis cuspidata) by its sharply pointed rostral teeth (versus blade-like), the first pair of rostral teeth being located near the rostral base, its tapering and broad rostrum, and a less developed lower caudal fin lobe.
The freshwater sawfish is distinguished from the dwarf sawfish (Pristis clavata) by the more anterior first dorsal fin position, the presence of a lower caudal fin lobe, and the rostral teeth being evenly towards the rostral tip (versus slightly closer to each other). In addition, the freshwater sawfish reaches a larger maximum size (6.0 m or larger versus 3.1 m total length) than does the dwarf sawfish.
The freshwater sawfish is distinguished from the smalltooth sawfish (Pristis pectinata) by the fewer average number of rostral teeth per side (14-23, versus 20-34), the broad and tapered rostrum, the presence of a lower caudal fin lobe, greater width of the pectoral fins, more robust body, and the position of the first dorsal fin origin anterior to the pelvic fins.
The freshwater sawfish is distinguished from the largetooth sawfish by its geographic range. The morphology of these two species is indistinguishable.
The freshwater sawfish is distinguished from the green sawfish (Pristis zijsron) by the fewer number of rostral teeth per side (14-23, versus 23-37), the position of the first dorsal fin origin anterior to that of the pectoral fins, and the presence of a lower caudal fin lobe. The freshwater sawfish also has a broad and tapered rostrum equipped with evenly spaced rostral teeth (versus an inter-tooth space between the last two teeth greater than two times the inter-tooth space of the first two teeth).
The dorsal surface of the freshwater sawfish is uniform yellowish-grey or brown in color, with yellowish-brown outer fin margins. Their rostral teeth are typically colored a dirty cream or yellow, contrasting with the darker hue of the dorsal rostral surface. The ventral surface of the body is colored a dirty cream.
Freshwater sawfish have very small oral teeth with rounded cusps that are close-set. All oral teeth are functional at the same time. Upper jaw teeth are arranged in 70 to 72 rows consisting of 115-127 teeth per row, while tooth rows of the lower jaw number 64-68 consisting of 122-140 teeth per row.
The body of the freshwater sawfish is covered with minute, close-set dermal denticles having leaf-shaped crown ridges and anterior furrows in all developmental stages except in embryos. The crown ridges are less prominent in large specimens. Denticles are similar on both the dorsal and ventral sides of the body. Denticles do not fully appear along the lateral edges of the rostrum until after the rostral teeth have fully emerged from the sockets in young freshwater sawfish. Rostral denticles of this species are similar in shape throughout the length of the rostrum, although the crown ridges change in morphology from the anterior portion to the posterior portion. These ridges flatten out gradually from the tip to the rostral base.
Size, Age & Growth
This species attains a maximum size of at least 6.0 m (19.7 ft) total length. Larger stated maximum sizes (up to 7.0 m or 23 ft) need confirmation.
Three mature males collected off Durban, Africa measured between 3.75 and 3.92 m (12.3-12.9 ft) and weighed between 180 and 188 kg (397-415 lb). Recently born freshwater sawfish measure 72-93 cm (28.3-36.6 inches). In a 2004 study of Western Australian freshwater sawfish, specimens of the first year class measured up to 91.2 cm (35.9 inches), a male specimen of 1.0 m (3.3 ft) was an estimated two years old, specimens of both sexes measuring 1.6 m (5.2 ft) were an estimated three years old, and specimens of both sexes measuring between 2.1 m (6.9 ft) and 2.3 m (7.5 ft) were an estimated four to five years of age. During the same 2004 study, a female that measured 2.2 m (7.2 ft) was tagged in the Fitzroy River, and was recaptured approximately five months later having grown 30 mm (1.2 inches) longer during that time.
In a 1991 study, a mature male taken from Papua New Guinea measuring 3.6 m (11.8 ft) had a calculated age of 44 years, while an immature male measuring 2.5 m (8.1 ft) was determined to have been 16 years old. These age estimates are markedly greater than any other age and growth study performed on sawfishes to date, leading one to speculate that the researchers may have misinterpreted the annual growth rings (termed 'annuli') of the vertebral centra.
Despite the freshwater sawfish's interesting mode of food gathering, using its rostrum in a side-to-side slashing motion to dislodge invertebrates from substrate and to stun schooling fishes, little is known about the feeding habits of this species. Reported food items of the freshwater sawfish include the marine catfish Arius graeffei, cherabin (Macrobrachium rosenbergii), shrimp, and small fishes. Additional prey species may include freshwater prawn such as Macrobrachium australiense, M. rosenbergi, and M. handschii.
Freshwater sawfish, like all sharks, skates, and rays, reproduce by means of internal fertilization. This species, like all rays, utilizes a strategy of embryo nourishment called aplacental yolk sac viviparity. With this strategy, the embryos are nourished only by their yolk sac, which provides energy for them to develop into fully functional young sawfish in utero. The embryos are nourished by yolk stored in a yolk sac, connected to the embryo by a yolk stalk and both of these structures are fully absorbed before the young sawfish are born.
The minimum age at maturity is not known for the freshwater sawfish, but preliminary evidence suggests that it may take as many as 20 years before an individual can reproduce. Size at maturity for female freshwater sawfish is about 3.0 m (10 ft) in total length. Males of this species mature at about 2.5 m (8.2 ft) or less. The gestation period of the freshwater sawfish is probably about five months, based on the closely related largetooth sawfish of the western Atlantic Ocean. Freshwater sawfish are capable of giving birth in freshwater conditions far up rivers and in contiguous lakes. Parturition is thought to occur late in the wet season (December-March) in the Gulf of Carpentaria (Australia). A reported litter size of four young has been reported, but litter size may range up to ten or more young. The sex ratio of the young has not been recorded. Recently born freshwater sawfish measure 72-93 cm (28.3-36.6 inches), and are probably born tail-first. The saw teeth of young sawfish do not fully erupt, and are also covered in a sheath of tissue, until after birth so as not to injure the mother. Young freshwater sawfish rostral teeth reach their full size proportionate to the size of the rostrum soon after birth. The reproductive cycle of the freshwater sawfish is still not documented, but the closely related largetooth sawfish has been reported to produce litters every other year.
Although adult freshwater sawfish have little or no natural enemies, smaller individuals may fall prey to sharks, and to saltwater crocodiles (Crocodylus porosus). The remains of this species have been found in the stomach of a bull shark (Carcharhinus leucas) in the Fitzroy River (Western Australia). When entangled in nets, this species becomes particularly vulnerable to predation.
The parasites Nonacotyle pristis and Pristonchocotyle papuensis (Hexabothriidae) were first described inhabiting the gills of a freshwater sawfish collected in Papua New Guinea. Another parasite of the freshwater sawfish is the copepod Ergasilus sp. (Ergasilidae), also found on the gills of the freshwater sawfish inhabiting the Daly River (Australia). This copepod species also inhabits the barramundi (Lates calcarifer), which may be its primary host. The newly described parasite species Neoheterocotyle darwinensis n. sp. is known to inhabit the gills of dwarf sawfish near Darwin, Australia, and this species may also use the freshwater sawfish as its host. Other species likely to use the freshwater sawfish as a host include monogenean helminths such as Erpocotyle caribbensis andPristonchocotyle intermedia, both inhabiting the gills of largetooth sawfish in Central America, and the cestode helminths Phyllobothrium pristis and Anthobothrium pristis, both inhabiting the spiral valve of largetooth sawfish in Central America. Other likely parasites include nematodes, protozoans, and trematodes. Likely areas of parasite inhabitation include the skin, gills, and digestive tract. The effects of these parasites on the freshwater sawfish are unknown.
The freshwater sawfish was first described in 1794 by John Latham in his article An essay on the various species of sawfish in the journal Transactions of the Linnaean Society of London. Latham described the species based only on a rostrum. Unfortunately, the type specimen (the rostrum) was later destroyed in a fire at the Royal College of Surgeon's Hunterian Museum. Synonyms for the freshwater sawfish include Pristis perotteti Müller & Henle, 1841 and the misspellingPristis perrotteti. Invalid synonyms of the freshwater sawfish include Pristis antiquorum Latham, 1794; Pristis canaliculataBloch & Schneider, 1801; Pristiopsis leichhardti Whitley, 1945; Pristis typica Poey, 1861; Pristis zephyreus Jordan & Starks, 1895; and Squalus pristis Linnaeus, 1758. Similarly, the name Pristis pristis (Linnaeus, 1758) does not appear to be a valid synonym of either Pristis microdon or Pristis perotteti, pending further taxonomic review. The current valid scientific name for the freshwater sawfish is Pristis microdon Latham, 1794. Pristis microdon and Pristis perotteti may be one and the same species, and these names have even been used interchangeably by various authors. Taxonomic study is badly needed to shed light on this naming uncertainty. The generic name Pristis is Greek for "saw." The specific name microdon is derived from the Greek word mikros meaning "small." The scientific name Pristis microdon refers to the shorter rostrum of the freshwater sawfish compared to that of most other sawfishes.
Prepared by: Jason C. Seitz